The invention relates to a harvester brake fluid vacuum filling system and method. The system comprises a brake oil can and a brake main pump; an oil outlet of the brake oil can is connected with an oil inlet of the brake main pump through a brake pipeline, and the system is characterized by further comprising a vacuum filling machine; a filling gun head of the vacuum filling machine is in clamped connection with an oil filling opening of the brake oil can in a seal manner; the filling gun head of the vacuum filling machine is clamped on the oil adding opening of the brake oil can, gas in the brake oil can, the brake pipeline, the brake main pump and an output pipeline of the brake main pump is subject to vacuum pumping through the filling gun head, brake liquid is injected in to the brake oil can in a pressured manner through the filling gun head, and oil in the brake oil can is sucked through the filling gun head until the height of the liquid level in the brake oil can reaches the set value. A hydraulic execution element does not need to loosened and fastened, the vacuum gun head is directly clamped on the filling opening of the brake oil can, vacuum pumping and filling can be finished, operation is more convenient, filling time is shortened, and the filling efficiency is effectively improved.